The invention concerns a filter element, in particular a coalescence element of the type comprising a metallic, perforated support tube, electrically nonconducting inner and outer filter layers located on internal and external sides of the support tube, and a plastic terminal disk into which a metal fastening screw is set.
Filter elements used to filter out solid particles and/or water from a liquid (such as automotive fuel) are known for example from German Patent No. 21 26 080. In the liquid flowing through the filter layers, in particular layers of hydrocarbons, a static electric charge is generated, which must be removed by way of the metallic parts of the filter element. Since the perforated support tube usually is made of metal, it is able to conduct the electric charge from the liquid.
The electric charge can be conducted via the terminal disk to a center spindle carrying the filter element or a metal fastening spider with which all of the end disks of the filter elements of a separator are connected. This requires that the end disks be made of metal and that an electrical connection be established between the support tube and the metal terminal disk. It is known to insert for this purpose a radially acting spring (for example, German Patent No. 33 25 526) into the end of the metal support tube, whereby an electrical connection is established to additional external and internal tubes, one of which is, in turn, connected electrically with the metal terminal disk.
In order to simplify and reduce the weight of filter elements, it has been proposed to form the terminal disks of plastic. If plastic terminal disks are used (see the "Crystal Clear" prospectus of the Facet Co.), the electric charge cannot be removed by way of the terminal disk, so that the removal of the electric charge is omitted when plastic terminal disks are employed.
It is an object of the present invention to provide a filter element, in particular a coalescent element having a plastic terminal disk wherein with little manufacturing and installation effort an effective removal of the electrical charge from the support tube can be carried out.